1. Field of the Invention
The present invention relates to a recording head discharging liquid such as ink.
2. Description of the Related Art
Inkjet recording apparatuses use nonimpact recording schemes, and have characteristics that they can record data in various recording media and at high speed, and make little noise during the recording. Thus, such inkjet recording apparatuses have been widely used as recording mechanisms as printer, word processor, facsimile, and copying machine.
Such inkjet recording apparatuses use ink discharge methods, including a representative one that uses heaters as recording elements. The representative method uses an inkjet recording head (hereinafter, also referred to as recording head) that has a recording liquid chamber provided with heaters and electrical pulses are applied to the heaters as recording signals. The heaters then generate discharge energy (thermal energy), which is given to a recording liquid to cause phase change thereof. At the time of phase change, the recording liquid bubbles (boils), so that the pressure of generated bubbles is used to discharge droplets of the recording liquid.
Japanese Patent Application Laid-Open No. 2002-19146 discusses an example of such recording head. FIG. 16 is a perspective diagram illustrating the recording head.
A recording head 1 in FIG. 16 has recording element substrates 2 and 3, each having a number of recording elements arranged thereon. The recording elements are each provided with discharge ports to discharge ink. Logic signals and a power source voltage are supplied to the recording element substrates 2 and 3 from an inkjet recording apparatus main unit (hereinafter, also referred to as recording apparatus main unit) through an electrical contact substrate 5 and an electric wiring member 4. As a result, driving circuits (logic circuits and voltage conversion circuits) in the recording element substrates 2 and 3 operate to drive predetermined recording elements for a predetermined period of time, hence ink is discharged from the discharge ports corresponding to the recording elements.
The logic signals each include “clock” as reference of logic circuit operation, “recording data” to determine recording elements to be driven, “latch signal” to temporarily store the recording data at a latch circuit that is one element of the logic circuit, and “heat enable signal” to determine a period of time to drive the recording elements.
In recent years, to further increase printing speed, a full wiring type recording head has been discussed, in which a large number of recording element substrates are arranged in zigzag and has a print width larger than that of a recording medium. In the recording head in FIG. 16, printing involves scanning of a recording medium by a recording head. In contrast, a full-wiring type recording head enables printing at high speed through single passing of a recording head, without scanning by the recording head, resulting in wide spread use of this type in recording apparatuses for business and industry.
Such full-wiring type recording head requires a large number of recording element substrates and also a large number of discharge ports to enable printing through one pass of the head without deterioration in image quality due to non-discharge of ink. Accordingly, formation of a large number of logic signal terminals is required to input/output logic signals, and a large number of logic signal lines are routed over an electric wiring member to transfer logic signals. Such structure may cause noise in the logic signal wiring.
For example, parallel logic signal lines may affect each other, causing capacitive coupling that induces noise. In general, longer and closer wiring causes capacitive coupling, and hence, in large-size recording heads such as those of full wiring type, noise is more likely to be induced.
In addition, a logic signal wiring located close to a power supply wiring where a large amount of current flows may be affected by induced noise. In a full wiring type recording head having a large number of discharge ports, as compared with recording head of smaller type, a larger number of recording elements are driven simultaneously, and a larger amount of current flows through power supply wiring that drives the recording elements, leading to induction of noise.
A logic signal affected by noise may lead to malfunction of logic circuits operated by the logic signals, and thereby recording elements may be driven at unexpected positions and timings, resulting in undesired discharge of ink and poor printing quality. In addition, highly responsive circuits for high frequency logic signals can react to noise, and thereby it is necessary to keep the high frequency logic signals from being affected by the noise.
To reduce influence of noise, high frequency logic signal wiring is required to be arranged not adjacent to the other high frequency logic signal wiring and power source wiring where a large amount of current flows. As described above, however, in a full wiring type recording head having a large number of logic signal wiring, not all of the high frequency logic signal wiring can be arranged as desired. Consequently, to reduce influence of noise, the spaces between the high frequency logic signal lines need to be increased, which eventually enlarges the electric wiring member, and eventually the recording head.